Field of the Invention
The present invention relates to a bronze alloy for a musical instrument having excellent acoustic characteristics, high strength and improved processability, through micronization of crystal grains by the addition of zirconium (Zr).
Related Background of the Invention
Cu—Sn-based copper alloys containing copper (Cu) and tin (Sn) as main components are known as bronze, and in particular, alloys in which a Sn concentration exceeds 20% by mass is referred to as bell metal from olden times. There are a cymbal and a church bell as traditional instruments, and the enhancement of a sound quality has been achieved by containing silver (Ag) or iron (Fe), from a long time ago.
In Cu—Sn-based copper alloys, the larger a Sn concentration becomes, the more acoustic characteristics are enhanced, but processing thereof becomes difficult. Therefore, when copper alloys in which a Sn concentration is 18% by mass or less are to be processed, a processing method such as rolling or forging is used. When copper alloys in which a Sn concentration exceeds 18% by mass are to be processed, casting processing is used. Until now, when trying to enhance quality of a musical instrument using a copper alloy and to obtain different acoustic characteristics, the improvement in a molding process and a shape of the instrument is carried out. However, copper alloys itself to be used for instruments have not largely improved, and copper alloys having a Sn concentration of 18% by mass or more and having improved processability are not proposed (refer to Patent Literature 1).
The present inventors have proposed the increase of a Sn concentration in a Cu—Sn-based copper alloy to 23% by mass from the viewpoint of putting importance on acoustic characteristics and the addition of titanium (Ti) that is an active metal in order to improve rolling and molding processability (refer to Non-patent Literature 1). It is possible to perform molding processing on a cymbal by enhancing processability of a bell metal material having a Sn concentration exceeding 18% by mass, and thus it becomes possible to develop instruments of high sound quality having a complex and profound sound. The technology of adding Ti that is an active metal to a Cu—Sn-based copper alloy was heretofore practiced by a vacuum melting method, but it becomes possible to realize Cu—Sn-based copper alloys having such a composition by using a manufacturing method that makes it possible to cast a copper alloy by melting a copper alloy material in the air (refer to Patent Literature 2; hereinafter referred to as the “Mizuta system”).
The metal structure of Cu—Sn-based copper alloys is an aggregate of crystals, and a part surrounded by a boundary surface of crystals (crystal grain boundary) is referred to as a crystal grain. The dimension of the crystal grain is generally represented by a crystal granularity or a crystal grain diameter. In a Cu—Sn-based copper alloy manufactured by the Mizuta system, although the processability is enhanced, the cross-sectional area of a crystal grain is as coarse as 1 mm2 to 10 mm2, and thus there is a problem in which the alloy is easily broken when being used as cymbals. Namely, it is considered that, since a hot rolling temperature of a Cu—Sn-based copper alloy containing 23% by mass of Sn having almost no processability is set to be high, the processing is performed at the secondary recrystallization temperature and the crystal grain has become coarse. As the result, the metal structure has become easily broken along the crystal grain boundary, and a cymbal may be broken depending on the magnitude of force of striking the cymbal or the method of striking the cymbal. As to the micronization of crystal grains, Patent Literature 3 describes that crystal grains are micronized by adding an element other than the main component such as Zr to a phosphor bronze alloy in semi-melting alloy casting process.